Rapid expansion and renormalization of parietal gray matter volume following associative learning

Abstract

The human brain exhibits rapid structural plasticity following learning, yet its temporal dynamics and behavioral relevance remain elusive, particularly for declarative forms of learning. In this study, we tested whether T1-weighted MRI captures rapid structural reorganization following associative memory formation and whether such changes follow an expansion-renormalization trajectory. We combined three independent datasets (N = 198) to quantify gray matter volume (GMV) changes following an associative memory task using voxel-based morphometry across baseline, 2 h, and 12 h post-learning. We observed transient GMV increases in parietal, lateral occipital, and cerebellar regions at 2 h post-learning, which were no longer detectable relative to baseline by 12 h, consistent with rapid renormalization. Critically, GMV changes in left parietal cortex were associated with memory retention, such that greater maintenance of GMV was associated with better retention. In a separate, spatially distinct effect, sleep facilitated renormalization of GMV in the right parietal cortex, an effect that showed no association with memory retention. Our findings provide evidence that human gray matter undergoes hour-scale changes, reflecting dissociable memory- and sleep-related components.